The invention is especially suitable for use in a high momentum, or high velocity burner which is designed to produce a high velocity flame or hot combustion products that are capable of creating high wind circulation, even during turndown of the burner. Such burners are intended to be used in high temperature furnaces, such as coil annealing, forging, or pipe heating furnaces, where the mechanical circulation of air is impractical or inefficient. As present, high momentum burners have within the burner block of refractory material, combustion chambers in which the air and fuel are burned. The resulting hot gases are discharged through a small opening with moderate velocity. The fluid pressure within such chambers is greater than atmospheric pressure.
Some of the disadvantages of using existing high momentum burners are, for example, that they require a special ratio control system to maintain a proper air-fuel ratio during turndown of the burner. The resistance and drop of pressure through the flue gas discharge opening changes as the burner firing rate is changed, thereby creating a variable back pressure in the combustion chamber, resulting in a variation of the air-fuel ratio. Moreover, the refractory material of the burning block is highly susceptible to cracking under pressure and, since the burner block or combustion chamber of such burners is greater than atmospheric or furnace pressure, a small crack in the burner block, or a slight leakage of fluid through any one of the many sealed holes communicating with the combustion chamber, can result in hot gas leakage or flame through the cracks. This can damage the burner or the ignition device and eventually reduce the efficiency and effectiveness of usage of the fuel. The invention is directed to overcoming the above deficiencies of currently available high momentum burners.
Briefly stated, the invention is in a high momentum burner wherein a flame or hot products of combustion are discharged at a high velocity, e.g. 300-500 miles per hour (mph). Means are provided for discharging an annular stream of air, under pressure, through an annular orifice at a predetermined velocity. A combustible fuel, such as natural or synthetic gas or oil, is radially directed into the annular stream of air for admixture with the air. A burner insert, having an opening in coaxial alignment with the orifice, coacts with the stream of air and fuel to increase the velocity of the stream through the opening for more intimate contact of the air and fuel and consequent thorough mixing in a first cylindrical chamber which abuts the insert. Means are provided for igniting the fuel in the mixing chamber. A second cylindrical chamber of greater diameter, abuts the first chamber and is designed to increase the temperature of the mixture of fuel and air and stabilize the flame as heated fluid or products of combustion pass through the second chamber. A third cylindrical chamber abuts the second chamber and is designed as a flame tunnel from which hot products of combustion pass at high velocities. The third chamber has a diameter which is greater than that of the first chamber but less than that of the second chamber. The chambers are coaxially aligned with the opening of the insert and are sized relative to each other so as to maintain therein, a fluid pressure which is less than the pressure of the atmosphere into which the flame or hot products of combustion are discharged from the burner.